1. Technical Field
Embodiments of present invention relate to an optical scanning device, a transport device, a feature detection device, a medium determination device, a sorting device, and/or a medium scanning method.
2. Related Art
In general, a transport device transporting a printing paper is incorporated in an ink jet printer (referred to herein as a “printer”). A transport device may include a function of optically scanning a transport medium, which is being transported, with an optical scanning device in order to control the transport of the transport medium and a function of detecting parameters relating to a transport state of the transport medium such as a transport speed or a transport amount of the transport medium. Also, a transport device may include a feature detection device that detects a feature such as an uneven pattern in a surface of the transport medium by optically scanning the transport medium and that specifies a type of a medium. In the optical scanning device that performs the optical scanning, in general, an optical sensor technology, as described in, for example, JP-A-2007-303975, may be used. In this case, a light receiving element of the optical sensor, such as a photosensor, receives the reflected light of incoherent light beams emitted from a light emitting element.
In a spatial frequency sensitivity of an optical scanning device, in general, a plurality of notches where sensitivity sharply declines at a specific frequency (or small range of frequencies) are present. The presence of the notches indicates that there is a possibility that some pieces of information to be acquired by the optical scanning device at the specific frequency or frequencies are missing. However, until now, research on restraining the occurrence of a notch in the spatial frequency sensitivity of the optical scanning device has not been sufficiently conducted. This type of problem is not limited to the optical scanning device used in the transport device of the printer and is a common problem to be solved in a technical field of the optical sensor in which optical scanning is performed using the photosensor. At least, the problem is a common problem in a feature detection device that uses optical scanning to detect a feature of a medium, and in a determination device that uses optical scanning to determine a type of a medium, and in a sorting device that uses optical scanning to sort the media by a type.